Audio amplifier



FIG. 1 is a front elevational view of an audio amplifier showing my new design;

FIG. 2 is a top plan view thereof;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a left side elevational view thereof; and

FIG. 6 is a right side elevational view thereof. 

The ornamental design for an audio amplifier, as shown. 